linux-kernel - Re: [Intel-gfx] [3.14.0-rc4] regression: drm FIFO underruns

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Date:	Tue, 13 May 2014 18:48:20 +0200
From:	Daniel Vetter <daniel@...ll.ch>
To:	Damien Lespiau <damien.lespiau@...el.com>
Cc:	Jörg Otte <jrg.otte@...il.com>,
	Ville Syrjälä 
	<ville.syrjala@...ux.intel.com>, David Airlie <airlied@...ux.ie>,
	intel-gfx <intel-gfx@...ts.freedesktop.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Dave Airlie <airlied@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [Intel-gfx] [3.14.0-rc4] regression: drm FIFO underruns

On Tue, May 13, 2014 at 05:46:31PM +0100, Damien Lespiau wrote:
> On Tue, May 13, 2014 at 06:38:32PM +0200, Daniel Vetter wrote:
> > > Doesn't work for me, I still have an underrun at boot-up.
> > 
> > I'm at a loss tbh with ideas. We successfully disable both pipes, then
> > enable pipe A and it all works.
> > 
> > Then we enable pipe B and _both_ pipes underrun immediately afterwards.
> > Really strange. Can you please reproduce the issue again on
> > drm-intel-nightly (latest -nightly should also have the display
> > corruptions fixed, so good to retest anyway) and attach a new dmesg with
> > drm.debug=0xe.
> > 
> > Meanwhile I'll try to come up with new theories and ideas.
> 
> I do remember a reporter saying a BIOS upgrade fixed that for him. This
> is one of the reasons Paulo put that BIOS update message.
> 
> It's worth the try if you ask me (the BIOS update will bring new memory
> latency values).

The fifo underrun code should be able to cope with bios stupidity - that's
why we don't enable it on takeover. Apparently there's a bug in that logic
somewhere.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
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